Plans were made in 1941 to build 1489 A-20Bs modified for
photo-reconnaissance and observation duties under the designation
O-53, but this project was cancelled in June of 1942.
Serials of O-53:
41-3670/5158 Douglas O-53 - heavy observation version of A-20.
American Combat Planes, Third Enlarged Edition, Ray Wagner, Doubleday,
McDonnell Douglas Aircraft Since 1920, Vol 1, Rene J. Francillon,
Naval Institute Press, 1988
United States Military Aircraft Since 1909, Gordon Swanborough and
Peter M. Bowers, Smithsonian, 1989.
A-20 Havoc in Action, Aircraft Number 144, Squadron/Signal Publications,
Jim Mesko, 1994.
War Planes of the Second World War, Fighters, William Green, 1964.
Boston, Mitchell and Liberator In Australian Service, Stewart Wilson,
Aerospace Publications, 1992.
Jane's Fighting Aircraft of World War II, Military Press, 1989.